Recently, there is an increasing demand for a high-definition large-screen display which is lighter, thinner and less-power-consuming for use in a TV set representing AV systems intended for home use or OA systems. To meet this demand, the development of the large-screen displays including a CRT (Cathode Ray Tube), an LCD (Liquid Crystal Display), a PDP (Plasma Display Panel), and EL (Electroluminescent) display, and an LED (Light Emitting Diode) all have be proceeding toward practical use.
The the liquid crystal display devices have advantageous features over other display devices in that liquid crystal display devices have the least depth (thickness); consume less power; and easily display full color images. Thus, liquid crystal displays have been applied to various fields, and the development of practical large-screen liquid crystal display devices has long been expected.
However, it is known that the mortality rate of liquid crystal display devices increases when the screen thereof is upsized. This is because of signal disconnection or imperfect pixels created during the manufacturing process. In addition, high cost is required due to the complicated process for manufacturing large-screen liquid crystal displays.
In order to eliminate these problems, multi-panel liquid crystal display devices have been proposed in which a large screen is provided by electrically and mechanically interconnecting a plurality of small substrates in a side-by side array. A problem arises, however, in that the joints between
However, when adopting the described liquid crystal display devices of the multi-panel display system, a problem arises in that the joints between the liquid crystal panels stand out due to a leakage of light through the mechanical connections between the sides of the substrates forming the array. Therefore, techniques for making these joints difficult to see are required in order to realize liquid crystal display devices which offer natural large screen images.
To achieve this a multi-panel liquid crystal display device in which the joints do not stand out has been proposed in Japanese Unexamined Patent Publication No. 122769/1996 (Tokukaihei 8-122769). FIG. 15 is a plan view showing a schematic structure of a liquid crystal display device 151 of the above publication. FIG. 16 is a cross-sectional view of the liquid crystal display device 151 taken along lines X--X.
The liquid crystal display device 151 has a plurality of active matrix liquid crystal panels 152. For simplicity of explanation, the following discussion will be limited to the interrelationship of two liquid crystal panels 152. It should be understood, however, that this discussion is included by way of illustration only, and that the interrelationships of the other adjacent pairs of liquid crystal panels is similar to the exemplary panel pair discussed below.
The liquid crystal panel 151 includes a TFT substrate 153 and a CF (color filter) substrate 154. The TFT substrate 153 and the CF substrate 154 are transparent glass substrates. On the TFT substrate 153, thin film transistors (not shown) are formed in a matrix. On the CF substrate 154, color filters 154a are formed in a matrix. By the described arrangement, an active matrix color liquid crystal panel 152 is realized. On the CF substrate 154, a black matrix (BM) 154b for separating respective pixels is formed. The black matrix 154b is made of a light absorbing film which shows a black color by absorbing light.
The described TFT substrate 153 and the CF substrate 154 are connected by a seal section 155 formed along the periphery thereof. Further, a liquid crystal 156 is sealed between the TFT substrate 153 and the CF substrate 154.
The liquid crystal panels 152 are connected by the bonding material 158. The liquid crystal panels 152 are connected on a large reinforcing substrate 157 also by the bonding material 158. As a result, the liquid crystal panels 152 are adjacently connected on the same plane.
For the bonding material 158 a transparent ultraviolet ray setting bonding material which is accelerated to be hardened with an application of an ultraviolet ray may be adopted. The bonding material 158 has the same refraction factor as the two glass substrates which constitute the TFT substrate 153 and the CF substrate 154. As a result, light, passing through the connecting section can be prevented from being refracted, reflected or scattered, thereby achieving unnoticeable joints.
On the entire outer surface of the reinforcing substrate 157, a polarizing plate (polarizing element) 159 is formed. On the entire outer surface of the liquid crystal panels 152, a polarizing plate (polarizing elements) 160 is formed. The respective polarizing axes of the polarizing plates 159 and 160 intersect at right angles.
On the outer surface of the polarizing plate 160, i.e., on the rear surface of the liquid crystal display device 151 (lower side of FIG. 16), a back light composed of, for example, a cold cathode tube (not shown) is formed. A driver (not shown) which controls an image signal is connected to the liquid crystal panels 152. The viewer can see the image information as input into the liquid crystal panels 152 by modulating the light from the back light in accordance with the image data as input.
Next, the method of manufacturing the liquid crystal display device 151 will be explained. FIG. 17(a) through FIG. 17(c) and FIG. 18(a) through FIG. 18(e) are cross-sectional views showing the processes of manufacturing the liquid crystal display device 151.
First, as shown in FIG. 17(a), a shielding members 161a is formed at a central portion with a predetermined width in a lengthwise direction of the cut surface on the connecting side of the liquid crystal panels 152. Next, as shown in FIG. 17(b), the liquid crystal panels 152 are connected in such a manner that respective shielding members 161a contact one another. Here, the shielding members 161a are connected so as to form a shielding film 161. Next, in the state where the liquid crystal panels 152 are connected via the shielding film 161 as shown in FIG. 17(b), and as shown in FIG. 18(a), a bonding material 158 having a viscosity in a range of from 100 to 1000 cP is injected in the spacing formed between the liquid crystal panels 152 so as to connect them. Thereafter, as shown in FIG. 18(b), the bonding material 158 is applied on the entire surface of the substrates of the liquid crystal panels 152.
Next, as shown in FIG. 18(c), the reinforcing substrate 157 and the liquid crystal panels 152 are connected via the bonding material 158. Here, the reinforcing substrate 157 is connected to the liquid crystal panels 152 gradually from one side so as not to enclose foams in the bonding material 158.
Thereafter, as shown in FIG. 18(d), the excessive bonding material 158a as being overflown from the spacing between the liquid crystal panels 152 and the reinforcing substrate is removed. Thereafter, as shown in FIG. 18(e), an ultraviolet ray is projected to the bonding material 158 from the side of the rear surface of the reinforcing substrate 157 so as to harden the bonding material 158.
However, when adopting the described techniques, the following problems 1 and 2 would arise.
1 In the conventional arrangement, in order to uniformly connect the liquid crystal panels 152 and the reinforcing substrate 157 so as not to enclose foams therein, overflow of the bonding material 158 from the space between the liquid crystal panels 152 and the reinforcing substrate 157 is required. Therefore, a large amount of the bonding material 158 is required to connect the liquid crystal panels 152 and the reinforcing substrate 157. In this case, the amount of the bonding material 158 to be hardened is around 1/10 of the bonding material 158. In other words, the amount of bonding material 158a which is wasted is approximately 9/10 of the total amount of bonding material 158.
Therefore, in the conventional technique, a substantial amount of bonding material 158 is wasted. This increases manufacturing cost thereby resulting in an increase in the wholesale and retail cost of the liquid crystal display device 151. 2 In the process of manufacturing the liquid crystal display device 151, an excessive amount of the bonding material 158a overflows from the peripheral portion of the space between the liquid crystal panels 152 and the reinforcing substrate 157 each time a pair of liquid crystal panels 152 is attached to a reinforcing substrate 157. Therefore, not only the process of removing the bonding material 158 as being overflow, but also the process of removing excessive bonding material 158a adhering the liquid crystal panels 152 and the reinforcing substrate 157, are required.
Accordingly, in the process of connecting a pair of liquid crystal panels, to a reinforcing substrate the process of removing the excessive bonding material adhering the liquid crystal panel and the process of removing the bonding material overflow at the peripheral portion of the bonding section are both required each time a multi-panel liquid crystal display device is manufactured. This significantly decreases the efficiency and speed of the manufacturing process, thereby resulting in poor mass production quantity operability. As this causes a problem of lowering the throughput in the manufacturing process of the liquid crystal panel, which results in poor mass production.
Additionally, since in the conventional arrangement the bonding material which connects the liquid crystal panels and the reinforcing substrate is exposed to the outside air at the peripheral portion of the bonding section, the desirable reliability of the bonding material cannot be obtained. overflow at the peripheral portion of the bonding section are both required each time a multi-panel liquid crystal display device is manufactured. This significantly decreases the efficiency and speed of the manufacturing process, thereby resulting in poor mass production quantity.